The invention relates to methods and apparatus for producing a combustible fuel, torrefaction of biomass, producing carbon dioxide offsets as well as an article of manufacture. The general need and description are included in the patent application above.
The need for a clean burning biomass fuel is of the utmost importance. A more practical or substantially improved method of making torrefied wood could lead to clean electrical power plants burning biomass.
Clean electricity made from carbon neutral biomass could replace over 80 percent of the fossil fuel in use today. At present approximately 40% of fossil fuel is used for electrical generation. Another 40% of fossil fuel is used for transportation due to internal combustion engines.
Over 50 years ago it was envisioned that nuclear electric power generating plants would produce enough clean energy for all electric needs plus energy for electric automobiles and mass transit systems. This was a great vision and someday, new nuclear and fusion energy technologies may be perfected to accomplish this dream. Nuclear plants have encountered too may contamination problems at this time to be considered practical and fusion energy systems may be 200 years away.
The need for an immediate solution to replace our depleting and air polluting fossil fuel energy sources is of the utmost importance. The increase in the use of non-renewable coal and oil requires an immediate replacement fuel to prevent severe economic, health and social problems. One solution is renewable solar energy that replaces the use of coal in electric power generating plants. This approach has not been widely utilized.
Fossil Fuel use for electric power plants, heat energy and transportation is continuing to increase at an alarming rate. Coal fired power plants use most of the coal and produce most of the fossil fuel air pollution. For each ton of carbon burned, 3.67 tons of carbon dioxide is generated. The global use of carbon emissions are over 7 billion tons per year and is expected to reach 14 billion tons per year by 2050.
The concentration of carbon dioxide in our atmosphere has increased over 35% since the late 18th century. The level is now at 379 parts per million by volume and climbing. Estimated increases in the last year are alarming.
Many scientists say the only real long term prospect for significantly substituting for fossil fuels is a breakthrough in harvesting solar power.
Over the last 25 years an improved fuel source using wood that has been heated in the absence of oxygen has received considerable attention. This treated wood is called torrefied wood (TW). Numerous attempts have been made to produce this high energy, low pollution fuel with very limited success. Even with all the various methods considered, none has been practical except the prior patent application by this inventor. Even though coal fired electric power plants have found that using some torrefied wood mixed with coal greatly reduces the air pollution generated, the high cost of producing consistent quality torrefied wood simply does not exist with all prior art methods of production.
Wood has been used as a fuel for thousands of years. Wet wood may contain over 50% water. When burned, incomplete combustion occurs and it uses a large portion of its energy to turn the water into steam and produces considerable smoke and thousands of forms of noxious gasses. Dry wood, as used in many fireplaces, may contain approximately 22 percent moisture. For any specific wood being burned, the dryer the wood being burned, the more complete the combustion. Dry wood burns cleaner than wet wood, but incomplete combustion still occurs, resulting in the formation of smoke, carbon monoxide and many volatile organic compounds and other undesirable air polluting gases. The pollution levels produced are unacceptable for most air pollution agencies. Some agencies are banning wood burning but accepting the use of wood pellets in special heaters because wood pellets typically contain less moisture (approximately 10%). However, a substantial amount of volatile organic compounds still exists in very dry wood. When wood pellets formed from dry wood are burned they can generate VOC's and other greenhouse gases.
Carbonized wood is a three thousand year old technology that has been looked at to help replace coal. However, the process is inefficient because, in part, it consumes too much energy. A very promising improvement in technology was developed in the 1980's by the French when they commercially converted wood into torrefied wood. Torrefied wood has most of the moisture and most volatile organic compounds (VOC's) driven out resulting in a high percentage of carbon content. In addition, the chemistry and structure of the wood itself is converted into a new form by continued exposure to heat. The French process used heat treatment by an inert gas to drive out the unwanted moisture and volatile organic compounds and stopped the process before it became carbonized. The torrefied wood burned clean but production costs were high along with a complex system with high potential for fires that prevented this from practical commercial use.
Several inventions since have tried to perfect and improve the torrefaction process by using high pressure steam, high temperature inert gas, superheated steam and other gas, pressure and vacuum methods. Some of these technologies claimed to improve efficiencies but all have failed to overcome the practical conversion of wood into torrefied wood in a simple, easy, quick, practical, safe, uniform and economic way. What these prior technologies accomplished was demonstration projects that showed how using torrefied wood in co-firing with coal could result in cleaner burning with less air pollution generated. Again, all prior art methods, except the prior patent application by this inventor, have been too complex, too expensive, and have not been practical for commercial use.
A number of prior art methods exist for producing torrefied wood. These methods all use inert gas, high pressure steam, or superheated steam in the heat treatment process. These prior art methods primarily use convection heat transfer between the wood surface and the heat source such as a steam or inert gas medium. Using any type of inert gas or steam involves large containment systems with large amounts of surface area, high equipment costs, high energy costs, slow treatment rates, and low overall operating efficiencies with resultant high production costs. Maintaining an oxygen free inert gas environment to these systems adds to the complexity and costs.
With all these prior art methods the systems and equipment has to be complex and large to contain the inert gas or stream heat transfer medium. The high operating pressures required with steam, sometimes over 600 psi, require heavyweight materials for construction of the required equipment and typically utilize batch processes rather than continuous processes. These convection batch systems are inefficient and costly to perform, thus, the final product produced by such convection systems is expensive.
The torrefied wood produced in all prior art methods does not contain the heat transfer fluid (HTF) of this inventors prior patent application. Thus, the heat content is less at about 8,000 to 9,000 Btu per pound.
Even though torrefied wood works extremely well, as a fuel in co-firing with coal to reduce pollution, very little has been produced due to the overall processing inefficiencies and high costs of all prior art systems.
The inventor's recent prior patent application on an immersion method of Torrefaction where wood pellets are immersed in a high temperature heat transfer fluid is an exception and substantial improvement over prior art methods. This method has many advantages but does use some HTF in the process. Where that is not desired, the new, indirect metal conduction to wood process, is a substantial improvement over all prior art.